1. Field of the Invention
The present invention relates generally to a relief valve assembly and more particularly, to an improved structure of relief valve assembly, which has a good sealing function.
2. Description of the Related Art
FIG. 1 shows a relief valve assembly according to the prior art. According to this design, the relief valve assembly comprises a casing 70, an one0way valve 80, and a relief control valve 90. The casing 70 has an input end and an output end. The one-way valve 80 has one end connected to the input end of the casing 70 and the other end connected to a fluid supply device (not shown) for guiding a fluid from the fluid supply device into the inside of the casing 70. The output end of the casing 10 is mounted with a pressure gage (not shown) that measures and indicates the fluid pressure inside the casing 70. Further, the casing 70 has a radial through hole 71 formed in the periphery in fluid communication between the input end and output end of the casing 70. The relief control valve 90 is installed in the radial through hole 71 of the casing 70, and can be controlled to discharge the fluid out of the casing 10.
The aforesaid relief control valve 90 comprises a guide tube 91, which defines a passage 92, a valve stem 93, which has a stem body 95 axially movably inserted into the passage 92, a head 94 fixedly connected to one end of the stem body 95 outside the guide tube 91 and adapted to seal the passage 92 of the guide tube 91, and a groove 96 extending around the periphery between the head 94 and the stem body 95, an O-ring 97 fastened to the groove 96, a spring member 98 sleeved onto the stem body 95 of the valve stem 93 and connected between one end of the stem body 95 of the valve stem 93 remote from the head 94 and a part inside the guide tube 91 to hold the valve stem 93 in the close position to block the passage 92 of the guide tube 91, and a control member 99 threaded onto one end of the stem body 95 of the valve stem 93 for pressing by hand to move the valve stem 93 from the close position to the open position to open the passage 92 of the guide tube 91.
The aforesaid relief valve assembly is still not satisfactory in function. Because the O-ring 97 is directly mounted in the groove 96 around the periphery of the valve stem 93 and kept in contact with the inside wall of the guide tube 91, the O-ring 97 may be retained to the inside wall of the guide tube 91 during an axial movement of the valve stem 93 between the close position and the open position, thereby causing the valve stem 93 unable to function normally (see FIG. 2). When a high-pressure fluid is continuously supplied into the casing 70, the O-ring 97 may be forced to deform Excessive deformation of the O-ring causes the formation of a gap in between the guide tube 91 and the valve stem 93, and the fluid will leak out of the relief control valve 90.
Therefore, it is desirable to provide a relief control valve, which eliminates the aforesaid problems.